This invention relates to a method and apparatus for removing the bubbles contained in a liquid delivered continuously, and more particularly to a method and apparatus in which the bubbles contained in a liquid are dissolved therein to eliminate them. The deposition of bubbles is also prevented when the liquid is used.
Various methods in which the bubbles in a liquid are removed by utilizing ultrasonic waves and in which deposition of bubbles is prevented are well known in the art. For instance, U.S. Pat. No. 3,904,392 discloses a method in which a vacuum chamber and a pressure chamber are provided in a liquid delivering path, and a liquid having bubbles to be removed (hereinafter referred to as "a bubble removal liquid" when applicable) is continuously supplied into each chamber. At the same time a vapor-liquid interface for allowing bubbles to surface is maintained in each chamber, and an ultrasonic wave is applied to the bubble removal liquid to remove the bubbles therefrom.
Hence, in this conventional method, first in the vacuum chamber, relatively large bubbles contained originally in the liquid and bubbles which have been dissolved in the liquid are deposited as a result of the decrease of the solubility caused by the reduction of pressure. They are collected in the vapor-liquid interface to be eliminated by the ultrasonic wave. Then, in the pressure chamber, relatively small bubbles which could not be eliminated in the vacuum chamber are dissolved in the liquid by the interaction of the increase of solubility and the ultrasonic wave so as to eliminate the small bubbles.
This method, however, has a principle drawback in that since a vapor-liquid interface exists in each chamber, the gas on the liquid surface is additionally dissolved in the liquid during the application of pressure. As a consequence the density of air in the liquid is increased, and when the liquid is delivered to, for instance, a coating section under the atmospheric pressure, the density of air in the liquid is supersaturated when compared with the saturation solubility of air with respect to the liquid. As a result the bubbles dissolved in the liquid are again deposited. Therefore, this method is not applicable to the removal of bubbles from a bubble removal liquid such as photographic emulsion liquid. In such a system if a film formed by using the photographic emulsion liquid has a single bubble, the film is classified as a film poor in quality; that is, the film cannot be used.
In order to prevent such deposition of bubbles, a different method of suitably controlling the pressure conditions and the level of the liquid surface has been proposed. However, the control operation is rather intricate and difficult to commercialize.
Each of the above-described vacuum and pressure chambers is in the form of a tank. Therefore, the liquid flowing into the chamber is not generally allowed to directly flow out of the chamber. That is, a larger part of the liquid is retained in the chamber, which results in the non-uniform flow of the liquid. Therefore, it is not preferable to apply the conventional method to the removal of bubbles from a liquid such as a photographic emulsion liquid where the retention time greatly affects the quality of a picture. Furthermore, the conventional method suffers from the drawback that bubbles cannot be removed uniformly.
Another example of the conventional ultrasonic wave type bubble removing method is a method of removing bubbles from silver halogenide photographic emulsion liquid disclosed by Japanese Patent Publication No. 5295/1976. In this conventional system, as shown in FIG. 1, a silver halogenide photographic emulsion 2 containing bubbles is supplied, under a pressure of 1.3 Kg/cm.sup.2 or higher, through a liquid conduit 7 into an ultrasonic wave liquid tank 9. The removal of bubbles is carried out by utilizing the ultrasonic wave vibration generated by an ultrasonic wave oscillator 11 on the bottom of the liquid tank.
This method is similar to the method of U.S. Pat. No. 3,904,392 described before in that the ultrasonic wave is applied directly to the bubble removal liquid and the bubbles are collected in the vapor-liquid interface in the bubble removing tank thereby to eliminate the bubbles. Therefore, in this method also, for the same reason described above, i.e. the vapor-liquid interface exists, the gas on the liquid surface is newly dissolved in the liquid. When the liquid is delivered from the bubble removing tank to, for instance, a coating section which is under the atmospheric pressure, the gas dissolved in the liquid is deposited as bubbles again.